The invention relates to a polyurethane acrylate or vinyl type polymeric material for coating optical fibers or for an optical fiber ribbon based on a fluorinated diol.
Optical fibers are known that comprise a double polymer coating constituted by a plasticized primary coating in contact with the glass fiber and surmounted by a secondary coating. That double coating protects the fiber from mechanical or chemical attack that may cause attenuation faults for optical transmission.
The adhesion of each coating to the intended support must be good and its physical properties must be compatible with the conditions under which the fibers are drawn, in particular with the draw rate and with the final use of the fiber. The primary coating must absorb microbending and any stresses on the glass. The secondary coating endows the fiber with its mechanical properties.
Currently, primary and secondary coatings are polyurethane acrylate type coatings that are light-cured by UV radiation.
European patent application EP-A-0 565 425 describes a fluorinated polyurethane acrylate type polymeric material for coating optical fibers based on at least one diol, a diisocyanate, and an acrylate, characterized in that at least one of said compounds contains fluorine and at least one of said compounds contains sulfur.
That material has good mechanical characteristics, in particular improved static fatigue strength. However, it employs a sulfur-containing diol, for example, which involves high production costs because of the intermediate thiol preparation step that leads to the production of by-products that must be eliminated. The problem is identical to that of the other sulfur-containing compounds used to prepare the material described in application EP-A-0 565 425.
Thus, a material is sought that possesses the same mechanical properties but which does not require the use of sulfur-containing products, in particular sulfur-containing diols.
The invention provides a polyurethane type polymeric material for coating optical fibers, based on at least one diol, a diisocyanate, and an ethylenically unsaturated compound, characterized in that the diol is a fluorinated diol with formula I:
CnF2n+1xe2x80x94Axe2x80x94CH2OCH2xe2x80x94C(CH2OH)2xe2x80x94R
where n is 2 to 20, and A signifies xe2x80x94CHxe2x95x90CH or xe2x80x94CH2CH2xe2x80x94, and R is an alkyl group containing 1 to 4 carbon atoms.
In one embodiment, the diol is unsaturated and corresponds to formula:
CnF2n+1xe2x80x94CHxe2x95x90CHxe2x80x94CH2OCH2xe2x80x94C(CH2OH)2xe2x80x94C2H5
In another embodiment, the diol is saturated and corresponds to formula:
CnF2n+1xe2x80x94CH2CH2xe2x80x94CH2OCH2xe2x80x94C(CH2OH)2xe2x80x94C2H5
In an embodiment, in formula I, R is C2H5.
In an embodiment, in formula (I), n is a whole number in the range 6 to 14 inclusive.
In an embodiment, in formula (I), CnF2n+1 results from a mixture and n is in the range 6 to 14 inclusive.
In an embodiment, in formula (I), n is in the range 6 to 8 inclusive.
In an embodiment of the material, the ethylenically unsaturated compound is an acrylate.
The invention also provides a method of preparing the material of the invention, comprising:
(i) a step of reacting the fluorinated diol with the diisocyanate to produce a fluorinated diisocyanate pre-polymer;
(ii) a step of reacting the fluorinated diisocyanate pre-polymer with a hydroxyl-containing ethylenically unsaturated compound.
The invention also provides a fiber coated with at least one layer of a material of the invention which is light-cured; in particular, this layer is the secondary layer.
In an embodiment, the material is light-cured in the presence of a diacrylate as a reactive diluent.
The invention also provides a method of drawing a fiber, comprising coating the fiber with a material of the invention, optionally mixed with a diacrylate as a reactive diluent, and a light-curing step.
In particular, the polymeric material of the invention is free of sulfur.
The diisocyanates and the ethylenically unsaturated compounds such as vinyl ethers and acrylates are compounds which are conventionally used in the field under consideration. These compounds may optionally be fluorinated. The diisocyanate can be replaced by a polyisocyanate, but for convenience, the first term will be used as the generic term. Examples of such diisocyanates, acrylates, and vinyl ethers can be found amongst the compounds cited in EP-A-0 565 425, including fluorinated compounds (as long as they contain no sulfur), and amongst the compounds cited in French patent application FR-A-2 712 291.
To prepare fiber coatings, the material of the invention, which also has the particular feature of being curable, is light-cured, in general by UV, preferably in the presence of a reactive diluent which is generally a diacrylate, present in a conventional amount.
Conventionally, photoinitiators and/or catalysts are used for the (photo) chemical reactions, if necessary.
The fluorinated diols used in the invention are novel.
The fluorinated diols of the invention, where R is C2H5, are prepared by radical reaction of CnF2n+1I with allyloxy trimethylol propane (or trimethylol propane monoallylether) followed either by dehydroiodation optionally followed by hydrogenaton, or direct reduction or hydrogenolysis.
While the description has been made with reference to the diol where R is C2H5, clearly other compounds are prepared in the same manner starting from the appropriate monoallylether. This monoallyl ether is the trimethylol alkane monoallylether, with the alkane corresponding to the group R increased by one carbon atom.
Radical addition can be carried out using known operating procedures, either in the solid state, or in an organic solvent, or in water.
Such radical addition has been described in German patent application DE-A-2 336 913, the reaction conditions of which can be followed.
The organic solvent can be acetone, tetrahydrofuran, dioxane, dimethylformamide, N-methyl-2-pyrrolidone, dimethylsulfoxide, methyl ethyl ketone, methyl isobutyl ketone, ethanol, isopropanol, or isopropyl acetate. Preferably, a hydrosoluble solvent or a mixture of hydrosoluble solvents is used.
Radical addition is normally carried out in the presence of initiator(s) which are used in an amount of 0.1% to 1.5% with respect to the total weight of the monomers used, preferably 0.1% to 0.5%. The initiators can be peroxides such as benzoyl peroxide, lauroyl peroxide, succinyl peroxide, or tert-butyl perpivalate, or azo compounds such as 2,2xe2x80x2-azobisisobutyronitrile, 4,4xe2x80x2-azobis(4-cyanopentanoic acid), and 2,2xe2x80x2-azobis-[2-methylbutanenitrile].
The reaction temperature range is wide, i.e., from ambient temperature to the boiling point of the reaction mixture. Preferably, a temperature of 60xc2x0 C. to 90xc2x0 C. is used; (thus avoiding polymer formation). Similarly, the allyloxy trimethylol propane can be added dropwise to control the reaction and limit the temperature rise.
An iodine-containing addition product is thus obtained.
Dehydroiodation is carried out using a strong inorganic base such as sodium or potassium hydroxide, or a strong organic base such as DBU (1.8-diazabicyclo(5.4.0)undec-7-ene). The reaction is preferably carried out in an aqueous medium. By way of example, the quantity of strong base used is close to the stoichiometric amount. The temperature is generally limited to about 70xc2x0-75xc2x0 C. (thus avoiding polymer formation).
This produces an unsaturated diol.
Saturated diols can be produced by different methods. They can be obtained from an addition product iodized by hydrogenolysis in the presence of an alkaline agent, or by reaction with sodium or zinc borohydride or lithium aluminum hydride or tributyl tin hydride. They can also be obtained from an unsaturated derivative by catalytic hydrogenation using known methods, either solvent-free or in solution in a conventional organic solvent such as ethanol or methanol, in the presence of a hydrogenation catalyst which, depending on the case, can be either Raney nickel or palladium on charcoal.
A saturated diol is thus obtained.
The perfluoroalkyl group CnF2n+1 can be linear or branched. The compound CnF2n+1I is known per se and is prepared using conventional methods.